This invention is directed generally to a fluid warming apparatus and, more particularly, to an apparatus for warming parenteral fluid such as whole blood under controlled temperature conditions for transfusion procedures and the like.
Generally, whole blood is stored under refrigerated conditions at temperatures of approximately 4.degree. C. to preserve the quality of the blood over extended periods of time. When the blood is to be infused into a patient, it is necessary that the blood be warmed to approximately 37.degree. C., the temperature of the human body, to avoid possible hypothermia and the attendant risk of ventricular fibrillation and cardiac systole. On the other hand, if the blood temperature is permitted to rise excessively during the warming process, the blood may coagulate or deteriorate.
For many surgical procedures, the quantity of blood which must be warmed for use during the procedure may vary widely. If a quantity of blood is warmed which is sufficient for all foreseen conditions, all of the warmed blood may not be used, resulting in waste of the excess blood since it generally cannot be refrigerated again. Also, for accident victims or other emergency cases, the time required to warm a large quantity of blood for transfusion may become a critical factor.
To heat a large quantity of blood, the blood may be warmed as it flows from a storage assembly to the patient. However, the required flow rate differs among the many surgical conditions and procedures. Indeed during the same surgical procedure, the flow rate of the blood may vary widely. For example, during a procedure a patient may suddenly hemorrhage so that the flow of blood into the patient must be drastically increased. After the hemorrhaging is stopped, the flow of blood may drastically decrease.
It is therefore desirable to be able to controllably warm widely varying flow rates of a fluid, such as blood, with the fluid then delivered to the patient at a generally constant, desired temperature. Additionally if the fluid has an upper temperature limit the heating should be accomplished without overheating and deteriorating the fluid.
Furthermore it is desirable to provide an apparatus which may be operated without undue complexity and have a control system capable of accurately heating the fluid to a desired exit temperature.
It is also desirable to provide an apparatus for warming fluid which incorporates safety features to prevent excess warming due to a malfunction in the control system. In addition, the temperature to which the fluid is being warmed should be readily apparent to operators and other attendant personnel.
Moreover, it is desirable to provide a blood warming device which simplifies any setup and operational supervision in using the device, so that the potential for misuse is reduced.
Due to the danger of the transmission of diseases by injection of a contaminated fluid into the body, it is very important that any fluid warmer not allow contamination of the fluid. Frequently a blood warmer will incorporate a disposable element such as a disposable tube or bag. The element completely contains the fluid as the fluid flows through the warmer.
It is desirable that any disposable element be easy to use with a "nondisposable" element of the warmer. Also if the disposable element is an element of the warmer generally described above, the element should be capable of handling varying flow rates without compromising the performance of the warmer. In addition any disposable element should have a small priming volume to reduce waste.
It is therefore an object of the present invention to provide an improved device for fluid warming. A related object is to provide such an improved device which is particularly adapted to warm, cold parenteral fluids such as whole blood for use during surgical procedures.
It is a further object of the present invention to provide an improved fluid warming device for warming blood and other parenteral fluids to a generally constant temperature over a wide range of flow rates.
It is another object of the present invention to provide an improved fluid warming device which is convenient to operate and requires a minimal amount of operator supervision.
It is a still further object of the present invention to provide an improved fluid warming device which requires a minimum setup time. Furthermore it is desirable that the setup be achieved efficiently and safely.
A still further object of the present invention to provide an improved fluid warming device wherein the element of the device which comes into contact with the fluid during the warming process is disposable.
It is also an object of the present invention to provide a disposable element which is configured to integrate with the operational characteristics of a nondisposable element of the improved warming device. A related object is to provide such a disposable element which can accommodate widely varying flow rates without compromising the operational characteristics of the improved warming device.
It is a still further object of the present invention to provide a disposable element which uses a small priming volume. A related object is that the disposable element facilitate the correct operational attachment to the nondisposable element.